Add the custom post term to the custom post title

You can try this (based on your unfinished PHP code)

if ( is_single() ) { 
    $terms_of_post = get_the_term_list( get_the_ID() , 'my-custom-term', '',', ', '', '' );
    $terms_of_post = strip_tags ( $terms_of_post );
    single_post_title(); 
    if( $terms_of_post ){
        echo ' (' . $terms_of_post . ')';
    }
}   

to get this format:

Title (term1, term2, term3)